Bloom filters didn't work reliably in 0.19.x and are a noop in 0.20.x. They should make a re-appearance in 0.21.x HBase.

== Historically ==

Bloom filters can be enabled on a per-column family basis in HBase. By specifying true for the bloom filter parameter in the constructor for H!ColumnDescriptor or by calling H!ColumnDescriptor.setBloomFilter(true), a [[http://portal.acm.org/citation.cfm?id=362692&dl=ACM&coll=portal|bloom filter]] as defined by Bloom in 1970 will be added to the column family.

This can be done either at table creation time or by disabling the table and modifying the column through the H!BaseAdmin.modifyColumn API.

Bloom filters are created using the mechanism specified by [[http://www.eecs.harvard.edu/~michaelm/NEWWORK/postscripts/BloomFilterSurvey.pdf|Broder and Mitzenmacher]] which computes the vector size using 4 hash functions.

Junit testing for bloom filters can be found in hbase.regionserver.!TestBloomFilters.

The HBase Wiki is in the process of being decommissioned. The info that used to be on this page has moved to http://hbase.apache.org/book.html#schema.bloom. Please update your bookmarks.